Process for preparing paving material



Aug. 18, 193,6. K. E. MCCONNAUGHAY 250515731 PROCESS FOR PREPARING PAVING MATERIAL Filed June 17,1952

KEN/YE TH E. P1 mrmuafm/g atenteci ug. 18, 1936 UNITED gSTATES PATENT OFFICE i PROCESS FOR PREPARING PAVING MATERIAL Kenneth E.. McConnanghay,

` assignor to Pre Cote Corporation, lis, Ind., a corporation of Indiana Indianapolis, Ind.,

Indianapo-I Application June 17, 1932, Serial No. 617,725 iclaims. (o1. S14- 43) This application is concerned with improvements in the apparatus and process of producing bituminous paving materials disclosed in my prior United States Patent was granted October 9, 1934.

In my prior application referred to, aggregate is immersed in liquefied bitumen, usually as.

phalt; and after being immersed is removed from the bitumen bath, and excess bitumen is permitted to drain from it. While this process has proven generally satisfactory with clean, dry, aggregate of a type to which asphalt will readily adhere, I find that with wet aggregates, with aggregates including a considerable proportion ofl extremely fine material, and with aggregates of a type to which asphalt does not readily ad.

here a better paving material is produced if the aggregate is subjected to a preliminary treatment before it is immersed in the bath of liqueiiedbitumen. This application is primarily conf cerned with apparatus suitable for administering such a preliminary treatment of aggregate and,

line 2-#2 of Fig. 1; and Fig. 3 is a side elevation partly in section, showing a modified form of mixer which may be used in carryingout the preliminary treatment.

The device'illustrated in the drawing embodies a" vat I0 adapted to contain a supply of liquefied bitumen, preferably an asphalt-water emulsion. Dipping into the .bitumen in the vat I0 is the lower end of a conveyor comprising a series of perforated buckets mountedon an endless chain I2, the chain |2 passing over a sprocket I3 disposedwithin the vat I 0. Preferably, the bottom of the vat is shaped sothat it closely conforms to the path of the outer edge of the buckets sothat the buckets will keep the vat substantially free from solid matter.

A I Mounted adjacent the vat I0 I provide an ag-V gregate hopper which may have two compartments l5 and I6.y The former compartment may be arranged to discharge aggregate directly into the vat I0, the rate of discharge being controlled W by a sliding gate Il. `If the compartment l5 is so used,` the' apparatus is adapted to perform theY No. 1,975,902 which process set forth in my prior application above'A referred to.

In carrying out the invention of the present` application, however, I employ the other hopper-4 compartment |6, which is arranged' so thatag` gregate may be fed from it into the outerendl of a trough 20, the inner endvof which discharges into the vat gregate to move along the trough 42i! andto be discharged into the vat VIll, I mayemploy a ro-v tatable shaft 2| carrying a series of helically disposed blades 22 which, asthe shaft is rotated, feed the aggregate along the trough toward and into the vat l0.' Y Y W For the purpose of feeding aggregate into the trough 20, I may mount in the bottom'ofthe hopper-compartment I6 a feed-'roll 25, `the upper.

surface of which is in contact with aggregatein the hopper I6. In the operation of theY device, the feed-roll 25 is rotated so that its upper Asurface moves toward a chute 26 leading downwardly into the trough 20. A sliding gate 21, movable toward andaway from the surface. of the roll 25 may be employed` to regulate therate at which aggregate is fed into the trough 20.

The present invention contemplates treating the aggregate with liquid treating agents-prior to its immersion in the vat pose, spray-bars 30 may veniently, these spray bars of the trough above the rotating blades 22 and discharge downwardly on to the aggregatepassing along the trough. In addition to the longitudinally extending spray bars 30, I may` employ,

Il); and vfor this .pur.

ifdesired, transverse spray bars 3| located in'v the chute 26.

If the liquid treatingagent discharged on the aggregate throughthespray-bars 30 and 3| is ofa bituminous nature, as it will be in' most cases, it maybe necessary, or at least advisable, to heat the blades 22 in on them of the mixture of aggregate and bitumen. To this end, the shaft. 2| `and blades 22 may be made hollow, and the ends and. steam-discharge aggregate through the blades 22 rather .than

If thisisdesvredf 55` through spray-bars 30 and 3|.

the outer end of the hollow shaft 2| 'may be closed,

l0. For the purpose of causing ag-.

beV employed. Con. extend longitudinally orderv to prevent` the. adhesion of bitumen to themand theicollection of the shaft' connectedA respectively with steam-discharge `and steam-v supply pipes 33 and 34. nInaddition, the trough steam-jacket 35 con.

as by means of a plug 40 illustrated in Fig. 3, and the blades 22 and shaft 2l provided with a multiplicity of holes. In such an arrangement, the Y liquid treating agent will be supplied through the 5 supply pipe 33, will pass through the hollow shaft 2| and will be discharged through the openings in that shaft and in the blades 22. Y If it is desired, as it may be in certain instances, to introduce into the trough 26 to be mixed with the aggregate a solid treating agent as well as a liquid treating agent, such result may be obtained through the use of a supplementary hopper 45 which is adapted to contain the solid material and which has mounted on or near its bottom a feed screw 46 discharging into the trough 20 as is clear from Fig. 2. The shaft 2 I roll 25, and screw 45 are convenientlyinterconnected to rotate jointly.

With the apparatus above described, variousA types of treatment may be employed vdepending upon the, type of aggregate, the type of bitumen, and thetype of finished material which it is de'- sired to produce. There are set forth below descriptions of several different modes of treatment 2.5, in conjunction with which the apparatus above described may be used.

Where the aggregateY employed in a process includes a considerable amount of dust or other fine material, the direct immersion method of 3Q my prior application above referred to is attended 'th certain diculties, as the fine material has a tendency to segregate. To overcome this, the apparatus above described may be used, a bituminous emulsion, or some other form of lique- S5fed bitumen being introduced either through ""the' spray-bars 30 and 3l or through the perforated blades 22. n they move the aggregate along the trough 2li thoroughly agitates the aggregate and provides 40 an even distribution of fine and coarse raggregate particles, the extremely fine particles being generally absorbed in the bitumen coating on the larger particles. Any film of dust or dirt adhering to theV large aggregate particles in their original state is knocked off. by the blades 22 and the bitumen is brought into direct contact with the surfaces of all particles.

`With certain kinds of aggregate, especially smooth-surfaced, hard aggregate, it has been Q noted that asphalt does not adhere readily to :"1" thesurface of 'the aggregate particles. It has also been noted that tar or tar emulsions or emulsions containing certain tar-distillates will readily adhere tothe surfacerof aggregate particles Vof a typeto which asphalt will not readily adhere. i Through the use of the apparatus Vdescribed in this application, the aggregate may be first subjected to treatment with tar or an emulsion of tar or suitable tar-distillates prior to its immersion l inthe Vat l0. When such a treatment of the aggregate is indicated,v tar or tar emulsion is introduced through the spray-bars 3U and 3|'. or through the hollow shaft and perforated blades.

A suitable tar emulsion may be one containing` from 60% to 80% tar, 20% to-40% water, and a small proportion of a suitable emulsifying agent. By` the action of the blades 22 this tarisfdistributed over the surfaces of all aggregate particles, adheres thereto, and provides an effective, theaggregate and the bitumenj bond between coating which is applied in the vat l0. Dependin g 'upon4 the size of the aggregate particles, 1%V to 37%of the tar emulsion, based on the Weight of the aggregate, may be employed. This process has the same advantages ,as that set forth in theV ,rb

The action of the blades as preceding example in respect to breaking up masses of ne aggregate particles and removing dust-coatings on the larger particles.

If the aggregate to be employed in producing the paving composition contains a large amount 5 of dust and is also damp, the dust will be bound by the moisture to the surfaces of the larger aggregate particles and will prevent contact of the bitumen in the Vat l0 with the aggregate particles. When such an aggregate is to be used, l0 therefore, I may introduce into the trough 20 a rather heavy emulsion of asphalt, say an emulsion comprising 65% to '75% of asphalt, '70 to 150 penetration, 25% to 35% water, and a small proportion of a suitable emulsifying agent. Because l5 of its comparatively high asphalt-content .such an emulsion would not be unduly thinned by the water in the aggregate and would combine such water and the dust in a film on each larger particle of aggregate; 20

The simple immersion process has proven to present some sliglitfdifculties when itis, used to. treat large-'particleaggregate, as it has been, diffey cult to build up a suiciently heavy bitumen film on the surface of the large-aggregate particles. 2,5 When treating s uch aggregate'with the device of this application, there may beintroduoed intothe, trough 20 a Vbituminous emulsion thickened by. the addition of lime-stoneior Vother stone dust. Or, instead ofadding the lime dust or other -lter 3D.- to the emulsion. and introducing'it intothe trough,Y suspended in the emulsion, an emulsion without. the filler may be used andtheller added tothe mixture through the use of the auxiliary hopper 5 and feed-screwl 46. Y In the latter method, the, 35E feed screw 45 is arranged.w to dischargeata pointintermediate the length of the trough 2, so that the bitumen and aggregate will-havev had an opportunity to becomeintermixed beforethe sand,

or other fine material is. brought into contact 40. with them.VY

Some aggregates are composedof particles hol/- ing extremely slick outer surfaces to which acorn-A paratively thick, soft, and sticky emulsionvvill adhere satisfactorily, but tov whichy an emulsion 45.. of the typeusually 'used inpaylng compositionsV will not adhere. In sucha case, I may introduce into the trough 20 an emulsion comprising, ap. proximately 65% to,'?5%` soft asphalt, say, 150.

6,350 penetration, 25% to.35% of water, and a, 59,

suitable emulsifying agent, About, 1%. to, 3%, based on the weightV of theaggregate, of such an, emulsion may. be, employed,` inthe trough. It ist distributed over, the aggregate particles bythetime they are dischargedinpthe bathinthe vat 55.;

l0. Y Y When it. isdesired toproduce apaving composition adaptedv to` be, stor'ed for a, period of several monthsbefore use@ mayV treat the ag, g'regate in the trough2` with afcomparatiyely. 60u thick emulsioncomllisingln to '15%^ of 'hard'. asphalt, 'say asphalt vof a penetration from50 to 80, 25%, to 3,5% of water, andasuitable.emul-y Srfyine' agent., Theamount of. emulsion used. should befrom 1% to 4% based onthe weight 65.v of the aggregate, and, following treatment of this, emulsionthe lcoated aggregate may be immersed in an emulsion Aofwa roadoil'orv uXing oil.Y The lightv emulsion will Yproduce a thin, film over the coated aggregate andvduringthe timethemate- 70:'

rial is stored will kflinwith,the, harder inner coating to produce anv ultimate asphaltlm havine-the desirednualit Y lf, for any reason, itii`s impracticablertof employ in the. Process, just; set forth an` asphalt.: 15iemulsion made by directly emulsifying the relatively hard asphalt, an emulsion of softer asphalt may be added to. the aggregate through the spray-bars or the hollow blades and the effective hardness of the total asphalt applied in the trough may be increased to the desired point by feeding powdered, extremely hard asphalt into the trough 20 through the use of the auxiliary bin 45 and feed-screw 46.

In general, the character of the bath in the vat l will be such as to supplement the preliminary treatment given the aggregate inthe trough 20. That is, the desirable characteristics and the proportion of the bitumen binder in the finished paving composition is well known, and the bitumen bath in the vat I0 should be of such a consistency and bitumen content as when mixed with the aggregate discharged from the trough it will produce a finished product meeting the required specifications. For example, if the aggregate is treated in the trough with a bitumen harder than that specified for the final composition, the bitumen in the vat I 0 will be softer than that specied in order that the mixture of the two bitumens will have the required properties. If the aggregate is treated in the trough with an emulsion rich in bitumen, and if that emulsion is not unduly diluted by moisture in the aggregate, the emulsion in the vat l0 will have a comparatively low bitumen content in order that the final bitumen film resulting from the blending of the separately applied emulsion will meet the desired specifications. Further, the immersion of the treated aggregate in the bath in the vat I il and its subsequent removal smooths out and evens the bitumen coatings applied to the aggregate in the trough 20.

It is not at all essential in all instances that the bituminous treating agent applied to the aggregate in the trough be different in character from that employed in the vat l0. Thus, if the aggregate does not require preliminary treatment with a particular kind of bitumen or with a bituminous emulsion. of a particular bitumencontent, but merely requires preliminary agitation such as might be required to prevent segregation of aggregate particles or to remove dustcoatings on the larger particles, an excess amount of liquefied bitumen might be supp-lied to the aggregate in the trough; such excess draining into the vat l0 and providing the bath therein.

I claim as my invention:

l. A process of producing a paving composition comprising a mixture of aggregate and a bituminous binder in predetermined proportions;

comprising agitating the aggregate While mixing it with a bituminous liquid containing less bitumen than the nished paving composition is to contain, immersing the aggregate in a bath of liquefied bitumen of diiferent characteristics from the first named bituminous liquid, elevating the aggregate from the bath, permitting excess bitumen to drain from it, and regulating the characteristics of the liquefied bitumen in the bath so that such predetermined proportionof bituminous binder is left upon the aggregate after excess bitumen has drained from it.

2. A process of producing a paving composition comprising a mixture of aggregate and a bituminous binder in predetermined proportions; comprising agitating the aggregate while mixing it with a bituminous liquid containing less bitumen than. the finished paving composition is to contain, immersing the aggregate in a bath of liquefied bitumen, elevating the aggregate from the bath, permitting excess bitumen tov drain from it, and regulating the characteristics of the liquefied bitumen in the bathso that such predetermined proportion of bituminous binder is left upon the aggregate after excess bitumen has drained from it.

3, A process of producing a paving composition comprising a mixture of aggregate and a bituminous binder in predetermined proportions;

comprising agitating the aggregate while mixing it with a bituminous liquid containing less bitumen than the finished paving composition is to contain, thereafter treating the aggregate with an excess of a second liquefied bitumen of different characteristics, then permitting excess bitumen to drain from the aggregate, and regulating the characteristics of said second liquefied bitumen so that such predetermined proportion of bituminous binder is left on the aggregate after the excess bitumen has drained from it. 4. A process of producing a paving cornposition comprising a mixture of aggregate and a bituminous binder in predetermined proportions; comprising agitating the aggregate While mixing it with a bituminous liquid containing less bitumen than the finished paving composition is to contain, thereafter treating theaggregate with an excess of a second liqueed bitumen, then permitting excess bitumen to drain from the aggregate, and regulating the characteristics of said second liquefied bitumen so that such predetermined proportion of bituminous binder isk left on the aggregate after the excess bitumen has drained from it.

KENNETH E. McCONNAUGI-IAY. 

